634640561 has 2 divisors, whose sum is σ = 634640562. Its totient is φ = 634640560.

The previous prime is 634640557. The next prime is 634640563. The reversal of 634640561 is 165046436.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 464833600 + 169806961 = 21560^2 + 13031^2 .

It is a cyclic number.

It is not a de Polignac number, because 634640561 - 2² = 634640557 is a prime.

Together with 634640563, it forms a pair of twin primes.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (634640563) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 317320280 + 317320281.

It is an arithmetic number, because the mean of its divisors is an integer number (317320281).

Almost surely, 2^634640561 is an apocalyptic number.

It is an amenable number.

634640561 is a deficient number, since it is larger than the sum of its proper divisors (1).

634640561 is an equidigital number, since it uses as much as digits as its factorization.

634640561 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 51840, while the sum is 35.

The square root of 634640561 is about 25192.0733763619. The cubic root of 634640561 is about 859.3615962489.

Adding to 634640561 its reverse (165046436), we get a palindrome (799686997).

The spelling of 634640561 in words is "six hundred thirty-four million, six hundred forty thousand, five hundred sixty-one".